1. Field of the Invention
This invention relates to a wind turbine and more particularly to a vertical axis wind turbine. Even more particularly, the invention relates to a vertical axis wind turbine wherein a wind vane is coupled to each blade which aims the blade into the air flow at a given angle of attack.
2. Description of the Related Art
Many types of wind turbines have been previously provided. Perhaps the most popular type of wind turbine is termed a horizontal axis wind turbine. In horizontal axis wind turbines, a large and heavy nacelle is mounted on the upper end of a robust tower which must have sufficient strength to withstand wind forces, rotational torque as well as being robust enough to support the weight of the generator and electrical equipment associated therewith. A horizontally disposed drive shaft extends from the nacelle and usually has three rotor blades secured thereto.
Many types of vertical axis wind turbines have also been previously provided. In the vertical axis wind turbines, a plurality of vertically disposed blades are attached to a vertically disposed drive shaft which is operatively coupled to a generator and associated with electrical equipment with the generator and associated electrical equipment usually being located on the ground near the wind turbine. For the vertical axis wind turbines to be efficient, the blades must be individually selectively pivoted about a vertical axis so that the blades are not disposed at an angle to the air flow, during the rotation of the entire blade assembly, which would “fight” or retard the rotation of the drive shaft by the other blades in the blade assembly.
Some of the designers of the vertical axis wind turbines have attempted to solve the above problem by employing a single wind vane which simultaneously causes pivotal movement of all of the blades of the blade assembly.
Applicant believes that vertical axis wind turbines are less expensive for a given power output than horizontal axis wind turbines for several reasons. First, the blades of a vertical axis wind turbine will be less expensive to fabricate than the blades of a horizontal axis wind turbine since the blades of the vertical axis turbine are of a uniform cross-section from end-to-end, are not tapered and are not twisted. The blades of a vertical axis wind turbine are also less expensive than the blades of a horizontal axis wind turbine since they can be made much lighter since they can be supported at both ends thereof.
Additionally, the blades of a vertical axis wind turbine will produce more power than the blades of a horizontal axis wind turbine since the entire length of the blades of the vertical axis wind turbine move at the maximum and uniform velocity through the air and since each blade crosses the wind path twice per revolution.
The tower of a vertical axis wind turbine is also less expensive than the tower of a horizontal axis wind turbine. Since the blades of a vertical axis turbine are never close to the tower, the tower can be supported with guy wires resulting in much lighter construction of the tower. The tower of a vertical axis wind turbine is never subject to a bending moment due to the gyroscopic reaction of turning a rotating mass (the blades) to follow a changing wind direction which is required in horizontal axis wind turbines. The tower of a vertical axis wind turbine is also less expensive than the tower of a horizontal axis wind turbine since the tower does not have to support the weight of complex and heavy generation equipment at the upper end thereof. Further, the tower of a vertical axis wind turbine does not require any nacelle support or yaw drive. In a vertical axis wind turbine, the generator and electrical equipment therefor is located at ground level and since the diameter of the generator is not restrained, the use of a large diameter slow-speed generator will eliminate the need for speed increased gearing.
Additionally, it is believed that vertical axis wind turbines are more efficient than horizontal axis wind turbines in that the frontal area thereof is rectangular rather than circular. In a vertical axis wind turbine, the entire mass of air flowing through the frontal area thereof is directed more uniformly thereby causing less turbulence to effect other turbines in the area. Additionally, the entire length of each blade passes through the air at the same velocity as opposed to horizontal wind axis wind turbines. Further, it is believed that vertical axis wind turbines will require less maintenance since there is no speed increasing gear box required nor is there any need for electrical or hydraulic sources needed for pitch and yaw control.